The present invention relates to a vehicular headlamp having a light source bulb of the xe2x80x9cH4xe2x80x9d type.
Many conventional vehicular headlamps employ a low-beam light distribution pattern Pxe2x80x2 as shown in FIG. 10, which has a horizontal cut-off line CL1xe2x80x2 and a diagonal cut-off line CL2xe2x80x2 rising from the horizontal cut-off line CL1xe2x80x2 at an angle of 15xc2x0. In this low-beam light distribution pattern Pxe2x80x2, the horizontal cut-off line CL1xe2x80x2 is arranged on the side of the oncoming lane and the diagonal cut-off line CL2xe2x80x2 is arranged on the side of the is lane in which the vehicle is traveling, whereby forward visibility for the driver is ensured while preventing the vision of drivers of oncoming vehicles from being dazzled by glare.
To obtain such a low-beam light distribution pattern, a light source bulb of the H4 type is often employed, which has a longitudinally extending filament 18a and a shade 18c covering the filament 18a around its axis at a central angle of approximately 165xc2x0 so that light beams emitted from the filament 18a in the downward direction are blocked. Due to the light-blocking effect of the shade 18c, light from the filament 18a does not impinge on a lower zone of a reflecting surface indicated by broken lines in FIG. 10.
In a vehicular headlamp designed to obtain the low-beam light distribution pattern described above, vertical aiming (beam adjustment) is carried out in the low-beam mode of the headlamp with respect to the horizontal cut-off line CL1xe2x80x2. For this reason, the contrast in luminosity of the horizontal cut-off line CL1xe2x80x2 should be sufficiently enhanced.
However, if the contrast in luminosity of the horizontal cut-off line CL1xe2x80x2 is enhanced excessively, long-distance visibility tends to decrease to such an extent that the driver may experience difficulty in driving in situations where the road ahead suddenly becomes dark, for example, in a case where the vehicle is approaching a flat road at the end of the descent of a slope. Also, even if the horizontal cut-off line CL1xe2x80x2 is slightly displaced upwards or downwards due to pitching of the vehicle or the like, there is a concern that oncoming drivers could be dazzled by glare.
The present invention has been made in consideration of such circumstances. It is an object of the present invention to provide a vehicular headlamp employing an H4 type light source bulb and which is capable of providing a low-beam light distribution pattern which makes it easy for a driver to drive and reduces the possibility of oncoming drivers being dazzled by glare.
The present invention achieves the above-stated object by the provision of an improved structure for securely supporting a light source bulb on a reflector, and by providing the reflector or a front lens with a suitable downward deflective reflection zone or a downward deflective transmission zone.
More specifically, a vehicular headlamp according to a first aspect of the present invention includes a light source bulb having a longitudinally extending filament and a shade covering the filament around its longitudinal axis at a central angle of approximately 165xc2x0 so that light traveling downward from the filament is blocked, a reflector securely supporting the light source bulb and having a reflecting surface forwardly reflecting light from the filament, and a front lens disposed forwardly of the reflector. The light source bulb is securely supported by the reflector so that left and right upper edges of the shade are at substantially the same height and the longitudinal axis of the filament is offset upward from the optical axis of the reflector at a predetermined angle. The reflecting surface of the reflector is provided with a downward deflective reflection zone which deflects downward and reflects light that has traveled from the filament past the vicinity of the upper edges of the shade and impinges on a traveling-lane-side reflection zone of the reflecting surface.
A vehicular headlamp according to a second aspect of the present invention includes a light source bulb having a longitudinally extending filament and a shade covering the filament around its axis at a central angle of approximately 165xc2x0 so that light beam traveling downward from the filament is blocked, a reflector securely supporting the light source bulb and having a reflecting surface forwardly reflecting light beam from the filament, and a front lens disposed forwardly of the reflector. The light source bulb is securely supported by the reflector so that left and right upper edges of the shade are at substantially the same height and the longitudinal axis of the filament is offset upward from the optical axis of the reflector at a predetermined angle. The front lens is provided with a downward deflective transmission zone which downwardly deflects and transmits light that has traveled from the filament past the vicinity of the upper edges of the shade and impinges on a traveling-lane-side reflection zone of the reflecting surface.
The aforementioned xe2x80x9cpredetermined anglexe2x80x9d means an angle is required to transform a generally sectorial light distribution pattern formed of light beams reflected from the reflecting surface of the reflector to a pattern where a pair of left and right cut-off lines constituting upper edges of the pattern at a central angle of approximately 195xc2x0 are both substantially horizontal, under the condition that the reflecting surface is a paraboloid of revolution extending around the optical axis of the reflector.
In the above-described vehicular headlamp of the present invention which has the light source bulb securely supported by the reflector so that the left and right upper edges of the shade are located at substantially the same height and that the longitudinal axis of the filament is offset upward from the optical axis of the reflector at the predetermined angle, under the condition that the reflecting surface of the reflector is a paraboloid of revolution extending around the optical axis of the reflector, a low-beam light distribution pattern is obtained which has horizontal cut-off lines formed of light beams reflected from the reflecting surface on laterally opposed sides of a vertical line perpendicular to the reference axis of the lighting fixture, hereinafter referred to as xe2x80x9cline Vxe2x80x9d.
In addition, with the reflecting surface of the reflector provided with the downward deflective reflection zone which downwardly deflects and reflects light that has traveled from the filament past the vicinity of the upper edges of the shade and impinges on the traveling-lane-side reflection zone of the reflecting surface, the front lens is provided with the downward deflective transmission zone which downwardly deflects and transmits light that has traveled from the filament past the vicinity of the upper edges of the shade and impinges on the traveling-lane-side reflection zone of the reflecting surface. Thus, in the aforementioned low-beam light distribution pattern, the oncoming-lane-side horizontal cut-off line formed of light reflected from the traveling-lane-side reflection zone is at a lower level than the traveling-lane-side horizontal cut-off line formed of light reflected from the oncoming-lane-side reflection zone.
In such a low-beam light distribution pattern, since vertical aiming can be carried out with respect to the traveling-lane-side horizontal cut-off line, the contrast in luminosity of the oncoming-lane-side horizontal cut-off line can be reduced.
This prevents long-distance visibility from being reduced when the road ahead of the vehicle suddenly darkens, for example, when the vehicle approaches a flat road after having traveled down a slope. As long as the horizontal cut-off line is just slightly displaced upward or downward due to pitching of the vehicle or the like, the luminosity of the upward light beams can be prevented from reaching a high level. Hence, the possibility of oncoming drivers being dazzled by glare is reduced.
In this manner, in a vehicular headlamp having a light source bulb of H4 bulb type, the present invention makes it possible to obtain a low-beam light distribution pattern which makes the vehicle easy to drive and reduces the possibility of oncoming drivers being dazzled by glare.
Moreover, since vertical aiming can be carried out with respect to the traveling-lane-side horizontal cut-off line as described above, it is also possible to set the target aiming position to a position where the horizontal cut-off line coincides with a horizontal line perpendicular to the lighting fixture reference axis, hereinafter referred to as xe2x80x9cline Hxe2x80x9d. By thus setting the target position, even without the use of special equipment for carrying out an aiming measurement, it becomes possible to carry out vertical aiming by means of a simple operation of making the traveling-lane-side horizontal cut-off line coincide with the height of the lighting fixture reference axis above ground level in a low-beam light distribution pattern directed onto a wall surface or the like in front of the vehicle.
As to the first aspect of the present invention, if the downward deflective reflection zone of the reflecting surface of the reflector is composed of a plurality of downward deflective reflecting elements having different downward deflection angles, the contrast in luminosity of the oncoming-lane-side horizontal cut-off line can be reduced sufficiently. Therefore it is possible to more effectively reduce the possibility of oncoming drivers being dazzled by glare.
In accordance with the first aspect of the present invention, if the reflecting surface of the reflector is provided with a horizontally deflective reflection zone which horizontally deflects and reflects light that has traveled from the filament past the vicinity of the upper edges of the shade and impinges on an oncoming-lane-side reflection zone of the reflecting surface, and if the horizontally deflective reflection zone forms a long-distance radiation light distribution pattern wherein oncoming-lane-side ends are substantially located on the line V, the long-distance visibility of the driver can be enhanced.
Further concerning the first aspect of the present invention, although the front lens may be formed of a translucent lens with all the functions of light distribution control allotted to the reflector, a plurality of lens elements may be formed in a predetermined zone of the front lens so that the front lens also performs the function of light distribution control. In the latter case, each of the lens elements may be designed to perform the function of downward deflective transmission or horizontally deflective transmission for compensating for the function of downward deflective reflection or horizontally deflective reflection performed by the reflecting surface of the reflector. Alternatively, each of the lens elements may be designed to exclusively perform another function (e.g., the function of lateral diffusion).
On the other hand, as to the second aspect of the present invention, if the downward deflective transmission zone is composed of a plurality of downward deflection lens elements having different downward deflection angles, the contrast in luminosity of the oncoming-lane-side horizontal cut-off line can be reduced sufficiently. Thus, it is possible to more effectively reduce the possibility of oncoming drivers being dazzled by glare.
Further concerning the second aspect of the present invention, if the front lens is provided with a horizontally deflective transmission zone which horizontally deflects and transmits light that has traveled from the filament past the vicinity of the upper edges of the shade and been reflected by an oncoming-lane-side reflection zone of the reflecting surface, and if the horizontally deflective transmission zone forms a long-distance radiation light distribution pattern wherein oncoming-lane-side ends are substantially located on a line V, the long-distance visibility of the driver can be enhanced.